I am unable to update my iPad to iPadOS 18.0.1

It is generally recommended that you maintain 4-6GB of free space at all times - as your iPad needs some temporary space to complete some tasks - such as performing system software updates.

A system software update requires sufficient space to be downloaded, unpacked and verified prior to installation - major version updates (such as updating from iPadOS 17.x to iPadOS 18) requiring considerably more space than an incremental point-update. After the update is successfully completed, temporary files are automatically deleted - returning free space.

If your internal storage is full, or is insufficient for the task that you need to perform, your only option is to better manage the storage that you have - and delete unused Apps or unneeded data. 

These support pages should prove to be helpful:

About storage on your device and in iCloud – Apple Support

What's the difference between device storage and iCloud storage? – Apple Support

Manage your iCloud storage – Apple Support

How to check the storage on your iPhone, iPad and iPod touch – Apple Support

Clear Other storage on your iPhone or iPad - Apple Support

“Offloading” Apps can be a helpful method of creating temporary space for a software update.

https://9to5mac.com/2020/01/21/how-to-offload-apps-in-ios-to-save-space-without-deleting-their-data/

Additional information about creating sufficient space for installation of a software update can be found here:

If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support

External storage options can often help with managing limited internal storage. Depending upon your iPad model, the iPad will either have a Lightning or USB-C port - and may therefore require either an Adapter or USB hub to connect the USB Storage device. If your iPad has a Lightning port, you’ll need an Apple Lightning to USB3 Camera Adapter:

• Lightning to USB 3 Camera Adapter

https://store.apple.com/uk/xc/product/MK0W2ZM/A

Try updating by connecting your iPad to a computer and updating that way.

Update software on iPhone, iPad, or iPod touch in iTunes on PC - Apple Support

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

That takes less room on your device.

Regards.

Tried again after a few hours and it installed on both iPads without any problems. The update was already downloaded so it was probably just a problem with Apple servers not verifying.

dyas03 wrote:

Thanks

But I use a windows PC and the Itunes only has podcasts & Audiobooks as an option.

iTunes for Windows PC has been superseded by the Apple Devices App:

https://apps.microsoft.com/detail/9np83lwlpz9k?hl=en-ms&gl=MS

Same here. It happened on both an iPad Air 5th Gen and an iPad Mini 5th Gen. Both have 20+ GBs of space. Battery was charged over 50% (or plugged in). Kept happening over and over. Seems to be a problem with the installer that affects some models or configurations.

I have experienced several issues with iOS 18.0.1. I personally recommend not upgrading right now until someone at Apple fixes it.